Microsoft Security Bulletin MS13-034 - Important

General Information

Executive Summary

This security update resolves a privately reported vulnerability in the Microsoft Antimalware Client. The vulnerability could allow elevation of privilege due to the pathnames used by the Microsoft Antimalware Client. An attacker who successfully exploited this vulnerability could execute arbitrary code and take complete control of an affected system. The attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. An attacker must have valid logon credentials to exploit this vulnerability. The vulnerability could not be exploited by anonymous users.

This security update is rated Important for the Microsoft Antimalware Client in supported versions of Windows Defender for Windows 8 and Windows RT. This security update has no severity rating for the Microsoft Antimalware Client in other Microsoft antimalware programs. For more information, see the subsection, Affected and Non-Affected Software, in this section.

The security update addresses the vulnerability by correcting pathnames used by the Microsoft Antimalware Client. For more information about the vulnerabilities, see the Frequently Asked Questions (FAQ) subsection for the specific vulnerability entry under the next section, Vulnerability Information.

Recommendation. Most customers have automatic updating enabled and will not need to take any action because this security update will be downloaded and installed automatically. Customers who have not enabled automatic updating need to check for updates and install this update manually. For information about specific configuration options in automatic updating, see Microsoft Knowledge Base Article 294871.

For administrators and enterprise installations, or end users who want to install this security update manually, Microsoft recommends that customers apply the update at the earliest opportunity using update management software, or by checking for updates using the Microsoft Update service.

See also the section, Detection and Deployment Tools and Guidance, later in this bulletin.

Knowledge Base Article

Affected and Non-Affected Software

The following software have been tested to determine which versions or editions are affected. Other versions or editions are either past their support life cycle or are not affected. To determine the support life cycle for your software version or edition, see Microsoft Support Lifecycle.

Does this update contain any non-security related changes to functionality?Yes. In addition to the changes that are listed in the Vulnerability Information section of this bulletin, this update includes other functionality changes as described in Microsoft Knowledge Base Article 2781197.

What is Windows Defender?Windows Defender is a free antimalware software that's now included in Windows 8. It helps protect a user’s computer against malware and other potentially unwanted software. Windows Defender provides real-time protection and anytime scanning options.

What versions of the Microsoft Antimalware Client in Windows Defenderdoes this update apply to?If the version of the Microsoft Antimalware Client is equal to or greater than version 4.2.223.0, then your client has already been updated and you do not need to take any further action. If the version of the Microsoft Antimalware Client is less than version 4.2.223.0, then you should install the update.

Is the Microsoft Antimalware Client updated with Microsoft Malware Protection Engine and malware definitions updates?No. Microsoft releases updates for the Microsoft Antimalware Client though standard distribution methods such as the Microsoft Update service. Updates for the Microsoft Antimalware Client are separate from updates to malware definitions.

I am using an older release of the software discussed in this security bulletin. What should I do?The affected software listed in this bulletin have been tested to determine which releases are affected. Other releases are past their support life cycle. For more information about the product lifecycle, see the Microsoft Support Lifecycle website.

Customers who require custom support for older software must contact their Microsoft account team representative, their Technical Account Manager, or the appropriate Microsoft partner representative for custom support options. Customers without an Alliance, Premier, or Authorized Contract can contact their local Microsoft sales office. For contact information, see the Microsoft Worldwide Information website, select the country in the Contact Information list, and then click Go to see a list of telephone numbers. When you call, ask to speak with the local Premier Support sales manager. For more information, see the Microsoft Support Lifecycle Policy FAQ.

Vulnerability Information

The following severity ratings assume the potential maximum impact of the vulnerability. For information regarding the likelihood, within 30 days of this security bulletin's release, of the exploitability of the vulnerability in relation to its severity rating and security impact, please see the Exploitability Index in the April bulletin summary. For more information, see Microsoft Exploitability Index.

This is an elevation of privilege vulnerability. An attacker who successfully exploited this vulnerability could execute arbitrary code in the security context of the LocalSystem account and take complete control of the system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. An attacker must have valid logon credentials to exploit this vulnerability. The vulnerability could not be exploited by anonymous users.

To view this vulnerability as a standard entry in the Common Vulnerabilities and Exposures list, see CVE-2013-0078.

Mitigating Factors

Mitigation refers to a setting, common configuration, or general best-practice, existing in a default state, that could reduce the severity of exploitation of a vulnerability. The following mitigating factors may be helpful in your situation:

An attacker must have valid logon credentials to exploit this vulnerability. The vulnerability could not be exploited by anonymous users.

In a Windows 8 default configuration, a standard user does not have permissions to write files to the root directory on the system. This mitigates the vulnerability because, in a default configuration, a standard user would not have the necessary permissions to exploit the vulnerability.

Workarounds

Workaround refers to a setting or configuration change that does not correct the underlying vulnerability but would help block known attack vectors before you apply the update. Microsoft has tested the following workarounds and states in the discussion whether a workaround reduces functionality:

Use this workaround to block attack vectors for the vulnerability on Windows 8 and Windows RT systems.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

Create a backup of the registry keys. Backup copies can be made using a managed deployment script by performing the following command as an administrator:

Run the registry script file you created in step 2 on the target system by using one of the following methods:

Method #1:

Double-click the Windefend_ImagePath_fix.reg file.

The following confirmation message should be displayed:

The keys and values contained in C:\temp\Windefend_ImagePath_fix.reg have been successfully added to the registry.

Method #2:

Alternatively, perform the following command as an administrator:

Regedit /s c:\temp\Windefend_ImagePath_fix.reg

Warning When using the command line method above, no confirmation message is displayed. You will not be notified as to whether or not the registry keys and values were successfully added to the registry.

Impact of workaround. None. This workaround changes the image pathname to the correct value.

How to undo the workaround.

Restore the backup file you created in step 1, above, by using one of the following methods:

Double-click the Windefend_backup.reg file.

The following confirmation message should be displayed:

The keys and values contained in C:\temp\Windefend_backup.reg have been successfully added to the registry.

Alternatively, perform the following command as an administrator:

Regedit /s c:\temp\Windefend_backup.reg

Warning When using the command line method above, no confirmation message is displayed. You will not be notified as to whether or not the registry keys and values were successfully added to the registry.

FAQ

What is the scope of the vulnerability?This is an elevation of privilege vulnerability.

What causes the vulnerability?This vulnerability is caused when improper pathnames are used by the Microsoft Antimalware Client.

What might an attacker use the vulnerability to do?An attacker who successfully exploited this vulnerability could execute arbitrary code in the security context of the LocalSystem account and take complete control of the system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.

An attacker must have valid logon credentials to exploit this vulnerability. The vulnerability could not be exploited by anonymous users.

What is the LocalSystem account?The LocalSystem account is a predefined local account used by the service control manager. It has extensive privileges on the local computer, and acts as the computer on the network. Its token includes the NT AUTHORITY\SYSTEM and BUILTIN\Administrators SIDs; these accounts have access to most system objects. A service that runs in the context of the LocalSystem account inherits the security context of the Service Control Manager. Most services do not need such a high privilege level. For more information, see the MSDN article, LocalSystem Account.

How could an attacker exploit the vulnerability?To exploit this vulnerability, an attacker would first have to log on to the system. An attacker could then run a specially crafted application that could exploit the vulnerability.

What systems are primarily at risk from the vulnerability?Windows 8 workstations are primarily at risk.

What does the update do?The update addresses the vulnerability by correcting pathnames used by the Microsoft Antimalware Client.

When this security advisory was issued, had this vulnerability been publicly disclosed?No. Microsoft received information about this vulnerability through responsible disclosure.

When this security advisory was issued, had Microsoft received any reports that this vulnerability was being exploited?No. Microsoft had not received any information to indicate that these vulnerabilities had been publicly used to attack customers when this security bulletin was originally issued.

For enterprise deployments as well as end users, typically the update is downloaded and installed via update management software or automatic updating.

End users can also manually update their antimalware client software by checking for updates using the Microsoft Update or the Windows Update service depending on the operating system and antimalware software. Refer to the following table for details:

You can verify that this update has been installed by verifying the version number for the Microsoft Antimalware Client.

If your version of the Microsoft Antimalware Client is equal to 4.2.223.0, then the update has been installed.

Note If the version of the Microsoft Antimalware Client is equal to or greater than version 4.2.223.0, then the antimalware program is not affected by the vulnerability and you do not need to take any further action.

Microsoft Active Protections Program (MAPP)

To improve security protections for customers, Microsoft provides vulnerability information to major security software providers in advance of each monthly security update release. Security software providers can then use this vulnerability information to provide updated protections to customers via their security software or devices, such as antivirus, network-based intrusion detection systems, or host-based intrusion prevention systems. To determine whether active protections are available from security software providers, please go to the active protections websites provided by program partners, listed in Microsoft Active Protections Program (MAPP) Partners.

Disclaimer

The information provided in the Microsoft Knowledge Base is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

Revisions

V1.0 (April 9, 2013): Bulletin published.

V1.1 (April 16, 2013): Bulletin revised to announce a detection change in the 2781197 package to correct a reoffering issue. This is a detection change only. Customers who have already successfully updated their systems do not need to take any action.

V1.2 (October 8, 2013): Bulletin revised to announce a detection change in the 2781197 package. This is a detection change only. Customers who have already successfully updated their systems do not need to take any action.